Flexural disc transducer



FLEXURAL DISC TRANSDUCER Filed Sept. 14. 1964 64 INVENTOR. 6 JOHN MBOUYOUCOS 56 571 573 584 W259 MHW F/g. 5 584 AGE/VT United States PatentO f 3,382,841 FLEXURAL DISC TRANSDUCER John V. Bouyoucos, Rochester,N.Y., assignor to General Dynamics Corporation, a corporation ofDelaware Filed Sept. 14, 1964, Ser. No. 396,168 7 Claims. (Cl. 116-137)This invention relates to transducers for the generation and radiationof acoustic energy, and particularly to a flexural disc transducer. In aflexural disc transducer, the member which radiates acoustic energy is adisc or plate which exhibits an elastic, flexural mode of vibrationrather than a rigid body piston-like motion.

Although the present invention is suited for more general applications,it is particularly adapted for use in deep underwater sound generators,as in the hydroacoustic transducers described in an application for aUS. Letters Patent, Ser. No. 151,516 entitled, ElectrmHydroacousticTransducer, and filed by John V. Bouyoucos on Nov. 10, 1961 now U.S.Patent 3,212,473 and in U.S. Letters Patent No. 3,004,512 entitled,Acoustic-Vibration Generator and Valve, issued Oct. 17, 1961, to JohnBouyoucos.

There exists a need for underwater sound generators which can withstandhigh hydrostatic pressure and deliver high acoustic power into thesurrounding water. In the above-mentioned US. patent application forElectro- Hydroacoustic Transducers, there as described varioushydroacoustic transducers wherein a radiating element constitutes apiston which moves as a rigid body connected to an elastic support whichacts as a spring. While such transducers have the advantage ofpresenting a uniform velocity distribution across a face of theradiating element, they often are comparatively heavy because of theamount of solid material necessary to provide adequate piston rigidity.

Patent No. 3,004,512 describes a thin spherical shaped Wall member thatvibrates in response to fluid pressure variations in the acousticgenerator. This wall member is adapted for transmitting or couplingacoustic energy into a surrounding body of water.

Bender plate or flexural disc transducers using piezoelectric materialsare known. However these transducers generally have limited powerhandling capability owing to the stress limitation of the ceramic usedtherein, or have limited depth capability due to stress limitations inthe plate or disc supporting member.

It is accordingly an object of the present invention to provide animproved sound generator having a flexural disc radiating element thattransmits high acoustic power to a surrounding fluid medium and is lightin weight and not subject to harmful stress levels.

It is another object of the present invention to provide an acousticvibration generator which is adapted either to radiate acoustic energyuniformly at relatively high energy density from a large surface area orto couple to a load acoustic energy having high energy density.

Another object of the present invention is to provide an acousticvibration generator having a relatively light coupling member whichprovides for eflicient power transfer between a sound generator and aload.

It is a more specific object of the present invention to provide atransducer which can sustain high hydrostatic pressure and still handlehigh acoustic power.

It is another object of the present invention to provide a transducerhaving a large power handling capability without the need for slidingfluid seals.

It is still another object of the present invention to provide animproved edge support for acoustic coupling members.

It is yet another object of the present invention to 3,382,841 PatentedMay 14, 1968 provide apparatus for decoupling an acoustic radiatingelement from its supporting structure.

Briefly described, a sound generator embodying the invention makes useof an improved flexural disc radiating element which provides largeacoustic power handling capability without the aforesaid disadvantage ofpiston or thin spherical shaped wall members. This flexural discradiating element also provides an acoustic transformer for transferringacoustic energy from a relatively small cross-sectional area to arelatively large cross-sectional area so that the impedances of anacoustic energy source and a load can be matched to each other.

The flexural disc radiating element in a preferred embodiment of thisinvention includes a unitary or monolithic structure having a flexuraldisc radiating portion, a peripheral mounting portion, and a thin shellor hollow, column-like structure connected between the radiating portionand the peripheral mounting portion. The flexural disc radiating elementhas two annular coaxial grooves located near the peripheral mountingportion of the disc, which grooves, in cooperation with the thin shell,separate and isolate the radiating portion from the peripheral mountingportion.

The two coaxial grooves are formed partway into the flexural discradiating element from opposite sides and at different radii in a sideby side relationship, so as to define the thin shell or hollowcolumn-like structure between the radiating portion and the peripheralmounting portion. One end of the thin shell is fixed and integral withthe peripheral mounting portion, while the other end of the shell isfixed and integral with the radiating portion. The thin shell isrelatively flexible for lateral forces or movement at the ends thereof,but is substantially rigid for end thrust or longitudinal forces. Thethin shell resists and is stiff to piston-like movement of the radiatingportion, but is compliant to flexing or bending movement at the edge ofthe radiating portion. Thus, the radiating portion can be forced into ahighly desirable edge-supported flexural mode of vibration for couplingacoustic energy from the generator to a surrounding fluid medium.

The monolithic structure eliminates the need for sliding hydrostaticseals. The flexural disc may be centerdriven or driven in a distributedmanner by various means such as a hydroacoustic or electroacoustic forcegenerator. One advantage of the invention is that a centerdriven allmetallic flexural disc radiating element is simple in design andconstruction and presents an extremely rugged interface to the externalenvironment. Another advantage resides in the fact that two flexuraldisc radiating elements may easily be mounted in a back to backrelationship to provide a double end radiating element. A furtheradvantage resides in the fact that the flexural disc radiating elementmay be flooded with a compliant liquid. In the latter case, the resonantfrequency of the transducer is determined by the combined stiffness ofthe radiating portion and its backing fluid and the total effective massof the moving system. Since a compliant liquid backed transducer isreadily pressure equalized to ambient pressure, such as .a transducer issuited for deep submergence application.

The invention itself, both as to its organization and method ofoperation, as well as additional objectives and advantages thereof, willbecome more readily apparent from a reading of the following descriptionin connection with the accompanying drawing in which:

FIG. 1 is a cross-sectional view, along a vertical central plane, of aflexural disc transducer in accordance with the invention;

FIG. 2 is a perspective view of another flexural disc transducer alsoembodying the invention, the transducer having a flexural disc radiatingelement;

FIG. 3 is an elevational view, partially in section of the transducershown in FIG. 2;

FIG. 4 is a sectional view, taken along a diametral plane, of theflexural disc radiating element shown in FIG. 2 in a rest or neutralposition;

FIG. 4a is a view similar to FIG. 4, of the flexural disc radiatingelement in an exaggerated position during a fiexural mode of operation;and

FIG. is a sectional view, taken along a diametral plane, of a flexuraldisc transducer employing electrostrictive ceramic elements for drivingthe flexural disc radiating element thereof in accordance with anotherembodiment of the invention.

FIG. 1 illustrates a hydroacoustic transducer 10 of the type describedin U.S. patent application, Ser. No. 151,516 mentioned above, whichincludes a flexural disc radiating element 12 secured to one end of astationary housing 13. Flexural disc radiating element 12 includes adrive piston 14. Drive piston 14 is contiguous to a drive cavity 18 ofthe housing 13 and moves axially in a cylindrical bore 15 in consequenceof acoustic pressure signals generated within drive cavities 18 and 19.These pressure signals are developed by a modulation of the flow of ahydraulic fluid through a variable area orifice 20 defined by a meteringrim 22 of a movable valve 23 and the corresponding rim 24 of an inwardlyextending pontion 25 of a stationary port structure 26. The hydraulicfluid enters under pressure at an inlet port 27 and passes through aninlet line 28 and through line branches 29 and 30 into drive cavities 18and 19. The direction of fluid flow is indicated in the various figuresof the drawing by arrows.

The branches 29 and 30 of FIG. I combine to form a loop 32 whichprovides an inertance in parallel with the acoustic compliance ofcavities 18 and 19. The fluid passes from cavity 18 through orifice 20and thence at reduced pressure into discharge chamber 34 whichcommunicates, through an outlet line 35, with a fluid exit port 36. Thevalve 23 is driven in a direction axially thereof along a path past thestationary port structure 26. An electromechanical force generator 38drives the valve 23. The generator 38 includes a moving coil 39 free tomove in magnetic field structure gap 40 when energized by an electricalcontrol input signal supplied to the coil 39 by way of a pair of leads42. The coil 39 is wound upon a portion of a spider 44 and the movementof the coil 39 is communicated to the valve 23 through a connecting rod45. If the resonant frequency defined by the mass of the moving systemand the stitfness of the spider is placed above the operating frequencyrange, the valve displacement will be directly proportional to and inphase with the input signal. In moving in reciprocal fashion within theport structure 26, the valve 23 cyclically varies the size of theorifice 20. A variational velocity disturbance or change in the velocityof the fluid generated by the size change at orifice 20 can give riseeither to compression or expansion of the fluid within drive cavities 18and 19 or to motion of the fluid within loop 32. The combination ofcavities 18 and 19 and the loop 32 thus constitutes an acoustic tankcircuit.

As the pressure variations in the cavity 19 are 180 out of phase withthe pressure variations in the cavity 18 at the nominal operatingfrequency, a point of zero pressure variation (acoustic ground) is foundalong the inertance loop 32. This point is used as the feed-in point forhydraulic fluid, thereby reducing the possibility of coupling energyfrom the acoustic tank circuit of the transducer back into theunidirectional flow source. Thus the line 28 terminates at the zeropressure point. The cavity 19, as shown in FIG. 1, is larger than thecavity 18; consequently, the zero pressure point along inertance loop 32will be nearer the larger cavity 19. It should be understood that thedrive cavities 18 and 19 may be of the same size in certainapplications. Because of the presence of the inertance presented by aloop 32, it

is possible to tune and resonate, independently of each other, theacoustic tank circuit and the load coupling circuit. The load couplingcircuit is made up principally of the effective mass of the fiexuraldisc 12 and the flexural compliance of the disc 12 associated therewith.The injection of fluid from orifice 20 into the parallel tank circuitresult in pressure variations therein which, in turn, operate on thesurface of the drive piston 14 to gener ate motion of the flexural discradiating element 12 against an external load, such as a body of water.

The fiexural disc radiating element 12 is made from a high strengthelastic material such as aluminum alloy 7G75-T6 having a composition of5.5% Zn, 2.5% Mg, 1.5% Cu and 0.3% Cr. The flexural disc radiatingelement is driven by a piston 14 which may be an integral part of thefleXural disc radiating element 12 or may be driven by various otherways as illustrated in FIGS. 3 and 5 and described hereinafter. Theflexural disc radiating element 12 (FIG. 1) comprises a radiatingportion 68 which includes the piston 14, a peripheral mounting portion61 and a hollow column-like portion which is in the shape of a thincylindrical shell 62. This shell 62 is defined by two coaxial circulargrooves 65 and 66 lo cated near the peripheral mounting portion 61 ofthe flexural disc radiating element 12. The coaxial grooves 65 and 66are blind, i.e. they extend only part way into the fiexural discradiating element 12 and from opposing sides. The grooves have differentdiameters; i.e., they are at different radii from the center of thedisc. The grooves are in side-by-side relationship so as to define thethin cylindrical shell 62. The thin shell 62 is connected to theradiating portion 60 at one end 63 and to the peripheral mountingportion 61 at the other end 64 of the thin shell 62 The thin shell 62provides an improved cylindrical edge support for the radiating portion60. The wall of the thin cylindrical shell 62 is substantiallyperpendicular to a radiating face 67 of the radiating portion 60; i.e.,the axis of the shell 62 is perpendicular to the face 67. The thin shell62 behaves in accordance to the physical laws governing thin cylindricalshells when subjected to end thrust and lateral forces applied to theends 63 and 64; that is, the thin shell 62 is stiff and highly resistiveto end thrust or to piston-like movement of the radiating portion 60.The thin shell 62 however is free to bend in response to lateral forcesexerted at its ends 63 and 64. The thin shell 62 is particularlycompliant to lateral forces generated at the end 63 when the radiatingportion 60 .is vibrated in a flexural mode.

The radiating portion 60 has a disc-like body similar to the radiatingportion 160 shown in perspective view in FIG. 2. The radiating portion60 has a diameter to thickness ratio which may be in the order ofapproximately 8:1. A fiexural radiating disc element 12 has been builtand operated with a radiating portion 60 having a diameter ofapproximately 17.5 inches and a thickness of approximately 2 inches. Thedimensions just given are for illustrative purposes only.

The peripheral mounting portion 61 is securely clamped to the housing 13by bolts 54. The peripheral mounting portion is shown as ring-like incross sectional area. However, the mounting portion 61 may have othershapes. An O-ring provides a seal between the flexur-al disc radiatingelement 12 and the housing 13. The peripheral mounting portion 61includes a series of mounting holes 67 for the bolts 54. The mountingholes 67 are uni formly spaced so as to provide an even clamping betweenthe mounting portion 61 and the housing 13.

When vibratory fluid forces are applied on the face 59 of drive piston14, the radiating portion flexes in a fiexural mode of vibration asthough that portion were supported along its circular edge. Theradiating portion 60 is forced into this flexural mode of vibration,since the edge support provided by the thin shell 62 is stiff to extension and compression and therefore offers :a high impedance topiston-like movement of the radiating portion 60 or to axial translationof the edge of radiating portion 60. The thin shell 62, however, ofierscomparatively negligible impedance to bending or to lateral movement ofthe edge of radiating portion 60. Freedom for bending yet high impedanceto piston action or axial translation provided by the ends 63 and 64 andby the thin shell 62 respectively, enables the flexural disc radiatingelement 12 to exhibit an edge-supported flexural mode of vibrationrather than a piston-like mode of virbation. 'Dhis edge-supported modeof vibration is characterized by an axial displacement of the radiatingportion 60, which starts at the end 63 of the thin shell 62 and reachesa maximum at the center of the radiating portion 60. The manner in whichthe radiating portion 60 and the thin shell 62 bends or flexes is shownin more detail in another embodiment of the flexural disc radiatingelement in FIGS. 4 and 4a, and will be described more in detailhereinafter.

In FIGS. 2 and 3 there is shown a single embodiment of a modification ofthe device of FIG. 1. Elements of the device of FIGS. 2 and 3corresponding to those of FIG. 1 are indicated by the same referencenumeral plus 100. The device of FIGS. 2 and 3 aside from certainmechanical assembly details differ essentially in that the flexural discradiating element 112 is backed with a compliant liquid instead of air.The drive piston 114 is shown as a free piston which is biased againstthe radiating portion 160 by a pressurized fluid in the chamber 118. Thedrive piston 114 includes an O-ring 153.

The transduced 110 of FIGS. 2 and 3 is particularly useful fortransducers which are submerged to a considerable depth in sea water.The pressure of the backing liquid within cavity 152 may be equalized tothe pressure of the sea in which the transducer 110 is submerged bymeans including a rubber diaphragm 77 trapped between two anchor members70 and 7-1 of an assembly 73 and attached by screws 74 to the portion 80of the housing 113. The rubber diaphragm 77 is exposed on one side toambient sea water passing through a perforated cover 76 Which also formsa portion of the assembly 73. The rubber diaphragm 77 is also exposed tothe fluid in the interior of the cavity 152 by means of a narrow passage85 in the portion 80 of the housing 113.

The flexural disc radiating element 112 is attached to the periphery ofthe portion 80 of the housing 113 by bolts 154.

The transducer 110 also includes a hydraulic input port assembly 91 andan output port assembly 92, which include flanges 93 and 94 connected to:a portion 95 of the housing 113 by bolts 96. The portion 95 of thehousing 113 is bolted to the enlarged housing portion 80 by .bolts 97.Acoustic pressure variations produced Within cavity 118 of thehydroacoustic amplifier 110 produces vibratory hydraulic forces on thedrive piston 114 which causes movement of the flexural dis-c radiatingelement 112 in a manner similar to that shown and described in FIG. 1,except, of course, the piston 114, while biased to remain in contactwith radiating portion 160, is not an integral part of the radiatingportion 160. The fluid within cavity 152 is isolated from the acousticamplifier drive cavity 118 by means of the O-ring 153 cooperating withdrive piston 114. Similarly, fluid leakage from cavities 118 and 152 tothe exterior of housing 113 is prevented respectively by O-rings 98 and155.

In the operation of the device shown in FIGS. 2-4a inclusive, thehydroacoustic amplifier 110 produces acoustic pressure variations in thecavity 118 in a similar way as described for the device of FIG. 1. Theaverage pressure in the cavity 118 biases the free piston 114 againstthe radiating portion 160 with sufiicient force so that piston 114 willremain in intimate contact with radiating portion 160 throughout thecycle of vibration. The alternating pressure variations in the cavity118 are transmitted thru the free piston 114 to the radiating portion160. The free piston 114 exerts :a dynamic force on the radiatingportion 160, which force is equal to the product of the alternatingpressure variations in cavity 118 and the cross-sectional area of piston114.

The radiating portion 160 is shown in FIG. 4 in a neutral or restposition. Shown at 99 are a plurality of uniformly distributed forcearrows representing a uniform load such as the hydrostatic ambient seapressure acting on a front face 158 of the radiating portion 160, whenthe back face 151 is, for example, in contact with air at atmosphericpressure, as might be the case in the structure 0 FIG. 1. The axis ofthe thin shell 162 and the grooves 165 and 166 are substantiallyperpendicular to the front face 158 of the radiating portion 160 so asto withstand high axial forces and yet be relatively compliant tobending moments acting at the end 163, as described previously for theflexural disc radiating element '60 of FIG. 1. The axial forces actingon the thin shell 162 are a summation of all the forces 99 acting normalto the face 158.

The static axial stress in the thin shell 1-62 is equal approximately tothe net axial static force exerted on radiating portion 160 divided bythe cross-sectional area of the thin shell 162, as established by itsdiameter and wall thickness. Once the axial force has been specified, asfor example, by specifying the maximum depth of operation, across-sectional area of the thin shell 162 can be selected to achieve asatisfactory stress level. The bending moment exerted by the thin shell162 on the edge of radiating portion 160, as well as the bending stressin thin shell 162, can then be controlled by the choice of the length ofthe thin shell 162. The ability to choose independently the shellthickness to contral axial stress, and the shell length to controlbending stiffness and bending stress is a particularly attractive andimportant feature.

When the hydroacoustic amplifier is operated, the drive piston 114 isresponsive to the alternating pressure in the cavity 118 and drives theradiating portion 166 into a flexural mode of vibration as previouslydescribed for. the radiating portion 60 of FIG. 1. FIG. 4a shows theradiating portion in an exaggerated flexural deflection to show thedisplacement of the radiating portion 160 across its faces 158 and 159and to show at the same time the displacement of the thin shell 162. Theradiating portion 160 flexes about its neutral axis While the thin shell162 flexes in a cylindrical plane which is substantially perpendicularto the neutral axis of the radiating portion 160. Effectively, itappearsthat the radiating portion 160 flexes substantially about .itsneutral axis along a line substantially midway between the ends 163 and164 of the thin shell 162.

FIG. 5 shows a flexural disc radiating element and electroacoustic drivemeans for driving the fiexual disc radiating element into a flexuralmode of vibration. Elements of the flexural disc radiating element ofFIG. 5 corresponding to those of FIG. 1 are indicated by the samereference numeral plus 500. The flexural disc radiating element 512comprises a radiating portion 560, a peripheral mounting portion 561,and a thin shell 562. The peripheral mounting portion 561 issubstantially similar to the mounting portion 161 of the flexural discradiating element 112 of FIG. 3. Mounting holes are provided at 554. Thethin shell 562 is encircled by two proximal grooves 565 and 566.

The radiating portion 560 includes two cavities 570 and 571 on faces 558and 559 respectively. Disposed in the cavities 570 and 571 arepiezoelectric members, such as electrostrictive ceramic discs 572 and573 respectively. The discs 572 and 573 are loaded tightly within thecavities 570 and 571 so that any radial expansion or contraction of theelec-trostrictive ceramic discs 572 and 573 will be translated intoflexural motion of the radiating portion 560. Electrostrictive ceramicdisc 572 includes flat electrodes 578 and 579 connected to inputterminals 580 and 581 respectively. Electrostrictive ceramic disc 72 ispolarized so as to expand and contract in a radial direction in responseto a varying AC signal applied to input terminals 586 and 581.

Electrostrictive ceramic disc 573 includes electrodes 583 vand 584connected to terminals 535 and 586 respectively. Electrostrictiveceramic disc 573 is also polarized to expand and contract in a radialdirection, in response to a varying AC signal applied to the inputterminals 585 and 586.

In the operation of the device of FIG. 5, and AC electrical input signalis applied to input terminals 580 and 581 of the electrostrictiveceramic disc 572 and to input terminals 584 and 535 of electrostrictiveceramic disc 573 in a manner well known to those skilled in the art sothat electrostrictive ceramic disc 572 Will expand and contract whileelectrostrictive ceramic disc 573 will contract and expand alternatelyduring each cycle of the AC electrical signal. In response to the phaseopposed radial expansion and contraction of electrostrictive ceramicdiscs 572 and 573 respectively, the radiating portion 560 is urged intoa flexural mode of vibration. The frequency of the vibrations is afunction of the frequency of the electrical input signal applied acrosselectrostrictive ceramic discs 572 and 573.

The device of FIG. 5 is particularly advantageous over prior art devicessince the flexural disc radiating element 512 incorporates an edgesupport for the electrostrictive ceramic discs 572 and 573 which may beexceptionally stiff for axial translation of the edge, yet whichprovides a low bending moment for the radiating portion 560 at its edge.The low stress inherent in the design of the peripheral mounting portion561 enables the electrostrictive discs such as 572 and 573 to be usedfor transducers which are subjected to high hydrostatic pressures.

Whereas the above examples have illustrated the use of hydroacoustic andelectrostrictive means as force generators to drive the flexural discradiating element of the invention, other force generators are equallyapplicable, such as moving coil, magnetostrictive, and purely mechanicalgenerators. Accordingly, the foregoing description should be taken asillustrative and not in any limiting sense.

What is claimed is:

1. A transducer comprising (a) a disc radiating element of elasticmaterial having a peripheral mounting portion and a disc-like radiatingportion,

(b) said disc radiating element including coaxial grooves on oppositefaces thereof encircling said radiating portion to define a thincylindrical shell therebetween connected,

(c) said thin cylindrical shell providing at one end thereof a lateralcompliant edge support for said one edge of said radiating portion, and

(d) means coupled to said radiating portion to excite said radiatingportion into vibration.

2. An acoustic vibration transducer comprising (a) a flexural discradiating element having a peripheral mounting portion and a disc-likeradiating portion,

(b) said disc-like radiating portion having two substantially paralleledges,

(c) said flexural disc radiating element including relatively deepproximal coaxial grooves on opposing faces thereof encircling saidradiating portion to define a thin cylindrical shell therebetween, saidshell having an axis substantially normal to at least one surface ofsaid radiating portion,

((1) said thin cylindrical shell providing at one end thereof an edgesupport for said one of said edges of said radiating portion,

(e) said shell having less impedance to lateral forces than tolongitudinal forces applied at said one edge, and

(f) means coupled to said radiating portion to excite said radiatingportion into vibrations.

3. An acoustic vibration transducer comprising (a) a disc-like radiatingelement of elastic material having a peripheral mounting portion and adisc-like radiating portion,

(b) means coupling the outer periphery of said mounting portion forproviding less impedance to a force in a direction along the surface ofsaid disc than to a force transverse to said surface, and

(c) means coupled to said radiating portion to excite said radiatingportion into vibrations.

4. An acoustic vibration transducer comprising (a) a flexural discradiating element having a peripheral mounting portion and a disc-likeradiating portion,

(b) said flexural disc element including relatively deep proximalcoaxial grooves on opposing faces thereof in a side by side relationshipto define a thin short cylindrical shell substantially normal to saidradiating portion,

(c) said shell being connected at one end to said peripheral mountingportion and at the other end to one edge around one face of saidradiating portion,

(d) said thin cylindrical shell providing a circular edge support forsaid radiating portion having less impedance to flexing of saidradiating portion than to piston-like movement of said radiatingportion, and

(e) means coupled to said radiating portion for exciting said radiatingportion into vibrations.

5. An acoustic vibration transducer comprising (a) a housing includingannular support means, at least a portion of said housing defining apath for the steady flow therethrough of a fluid medium under pressure,

(b) fluid chamber means,

(c) fluid flow switching means including a movable valve interposed insaid path for modulating repetitively the flow of fluid through saidchamber means, the movement of said valve converting a portion of thesteady flow energy into acoustic vibrations within said chamber means,

(d) a drive member set in motion in response to said acousticvibrations,

(e) a flexural disc radiating element having a peripheral portionrigidly secured to said support means,

(f) said disc element also including a radiating portion and a thincylindrical shell portion integral with said disc,

(g) said thin shell portion being connected to said peripheral portionat one end thereof and being connected to said radiating portion at theother end thereof,

(h) said drive member operatively engaging said radiating portion ofsaid disc, and

(i) said radiating portion being set into vibration in consequence ofthe motion of said drive member.

6. An acoustic vibration transducer comprising (a) a housing includingannular support means, at least a portion of said housing defining apath for the steady flow therethrough of a fluid medium under pressure,

(b) fluid chamber means,

(6) fluid flow switching means including a movable valve interposed insaid path for modulating repetitively the how of fluid through saidchamber means,

(d) the movement of said valve converting a portion of the steady flowenergy into acoustic vibrations Within said chamber means,

(e) a drive element driven in response to said acoustic vibrations,

(f) a flexural disc radiating element having a peripheral portionrigidly secured to said support means,

(g) said disc further including a radiating portion and a thincylindrical shell integral with said disc element,

(h) said radiating portion and said thin cylindrical shell beingdisposed within said peripheral portion of said fiexural disc radiatingelement and formed by closely spaced oppositely directed coaxial grooveswithin said disc element,

(i) said grooves being disposed along different radii on said discelement,

(j) said drive element operatively engaging said radiating portion ofsaid disc element, and

(k) the diameter of said radiating portion being long compared to thethickness dimensions of said radiating portion.

7. A transducer comprising (a) a flexural radiating element havingperipheral mounting portions and a radiating portion,

(b) said flexural radiating element including spaced apart grooves onopposite faces thereof encompassing at ieast a part of said radiatingportion to define thin columns interconnecting said radiating portion tosaid peripheral mounting portions,

(c) said thin columns providing at one end thereof an edge support forsaid radiating portion, and

(d) means coupled to said radiating portion to excite said radiatingportion into vibrations.

References Cited UNITED STATES PATENTS LOUIS J. CAPOZI, PrimaryExaminer.

1. A TRANSDUCER COMPRISING (A) A DISC RADIATING ELEMENT OF ELASTICMATERIAL HAVING A PERIPHERAL MOUNTING PORTION AND A DISC-LIKE RADIATINGPORTION, (B) SAID DISC RADIATING ELEMENT INCLUDING COAXIAL GROOVES ONOPPOSITE FACES THEREOF ENCIRCLING SAID RADIATING PORTION TO DEFINE ATHIN CYLINDRICAL SHELL THEREBETWEEN CONNECTED, (C) SAID THIN CYLINDRICALSHELL PROVIDING AT ONE END THEREOF A LATERAL COMPLIANT EDGE SUPPORT FORSAID ONE EDGE OF SAID RADIATING PORTION, AND (D) MEANS COUPLED TO SAIDRADIATING PORTION TO EXCITE SAID RADIATING PORTION INTO VIBRATION.